U.S. patent number 5,178,739 [Application Number 07/765,651] was granted by the patent office on 1993-01-12 for apparatus for depositing material into high aspect ratio holes.
This patent grant is currently assigned to International Business Machines Corporation. Invention is credited to Michael S. Barnes, John C. Forster, John H. Keller.
United States Patent |
5,178,739 |
Barnes , et al. |
January 12, 1993 |
Apparatus for depositing material into high aspect ratio holes
Abstract
A sputter deposition system includes a hollow, cylindrical
sputter target 14 disposed between an end sputter target 12 and a
substrate 19, all of which are contained in a vacuum chamber 20. A
plurality of magnets 24 are disposed outside the chamber 24 to
create intense, plasma regions 48 near the interior surface of the
cylindrical target 14 and thereby causing ionization of sputtered
neutrals. Rf power is inductively coupled into the chamber 24
through rf coil 16 to sustain the plasma and substrate 19 is
electrically biased to control ion directionality and energy.
Inventors: |
Barnes; Michael S. (Mahopac,
NY), Forster; John C. (Poughkeepsie, NY), Keller; John
H. (Newburgh, NY) |
Assignee: |
International Business Machines
Corporation (Armonk, NY)
|
Family
ID: |
27085518 |
Appl.
No.: |
07/765,651 |
Filed: |
September 25, 1991 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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607431 |
Oct 31, 1990 |
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Current U.S.
Class: |
204/192.12;
204/298.06; 204/298.08; 204/298.21 |
Current CPC
Class: |
C23C
14/345 (20130101); C23C 14/35 (20130101); C23C
14/358 (20130101); H01J 37/3405 (20130101); H01J
37/342 (20130101); H01J 37/3438 (20130101); H01J
37/3452 (20130101) |
Current International
Class: |
C23C
14/35 (20060101); H01J 37/34 (20060101); H01J
37/32 (20060101); C23C 14/34 (20060101); C23C
014/34 () |
Field of
Search: |
;204/192.12,298.06,298.08,298.16,298.17,298.18,298.12,298.19,298.21
;427/250,255.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Yamashita, "Fundamental . . . apparatus", J. Vac. Sci., Technol.,
A7(2), Mar./Apr. 1989, pp. 151-158..
|
Primary Examiner: Nguyen; Nam
Attorney, Agent or Firm: Romanchik; Richard A.
Parent Case Text
This is a continuation application of copending application Ser.
No. 607,431 filed Oct. 31, 1990, abandoned.
Claims
We claim:
1. An apparatus for depositing a material onto a substrate in a
vacuum chamber comprising:
sputtering means for providing a sputtering source of the
material;
magnetic means for providing a multidipole magnetic field for
magnetic confinement of plasma electrons;
rf energy transmission means disposed in the vacuum chamber for
inductively coupling rf electrical energy into the vacuum chamber
directly for producing a plasma of sufficient density and volume in
the vacuum chamber to cause ionization of sputtered atoms; and
substrate placement means for placing the substrate in contract
with said plasma.
2. The apparatus for depositing a material onto a substrate in a
vacuum chamber as defined in claim 1, further comprising biasing
means for electrically biasing the substrate with DC or rf energy
for controlling the energy and direction of ions impinging on the
substrate.
3. The apparatus for depositing a material onto a substrate in a
vacuum chamber as defined in claim 1, wherein said sputtering means
comprises:
a first sputter target;
a second sputter target disposed between said first sputter target
and the substrate; and
first and second sputter power source means for providing
electrical energy to said first and second sputter targets
respectively to cause sputtering thereof.
4. The apparatus for depositing a material onto a substrate in a
vacuum chamber as defined in claim 3, further comprising means for
varying the power between said first sputter target and said second
sputter target in order to adjust the uniformity of deposition over
the surface of the substrate.
5. An apparatus for depositing a material onto a substrate in a
vacuum chamber as defined in claim 1, wherein said sputter means
comprises:
a first sputter target;
a second cylindrical, hollow sputter target disposed between said
first sputter target and the substrate; and
first and second sputter power source means for providing
electrical energy to said first and second sputter targets,
respectively, to cause sputtering thereof.
6. The apparatus for depositing a material onto a substrate in a
vacuum chamber as defined in claim 5, further comprising means for
varying the power between said first sputter target and said second
sputter target in order to adjust the uniformity of deposition over
the surface of the substrate.
7. The apparatus for depositing a material onto a substrate in a
vacuum chamber as defined in claim 1, further comprising:
gas means for providing gas in the vacuum chamber, said gas having
an atomic mass greater than the atomic mass of the material.
8. The apparatus for depositing a material onto a substrate in a
vacuum chamber as defined in claim 1, wherein said rf energy
transmission means comprises:
rf power supply means for providing said rf electrical energy;
and
rf coil means for transmitting said rf electrical energy into said
plasma.
9. The apparatus for depositing a material onto a substrate in a
vacuum chamber as defined in claim 1, wherein said rf energy
transmission means comprises:
rf power supply means for providing said rf electrical energy;
rf coil means for inductively coupling said rf electrical energy
into said plasma; and,
magnetization means for magnetizing said rf coil means, wherein
said magnetization means confines plasma away from at least part of
said rf coil means.
10. The apparatus for depositing a material onto a substrate in a
vacuum chamber as defined in claim 1, wherein said rf energy
transmission comprises:
rf power supply means for providing said rf electrical energy;
a hollow rf coil means for inductively coupling said rf electrical
energy into said plasma; and
at least one magnet disposed within said hollow rf coil means for
confining plasma away from at least part of said hollow rf coil
means.
11. The apparatus for depositing a material onto a substrate in a
vacuum chamber as defined in claim 1, wherein said rf energy
transmission means and said sputtering means comprises:
rf coil means;
sputter power source means for providing electrical energy to said
rf coil means to cause sputtering thereof;
rf power source means for providing said rf electrical energy to
said rf coil means to cause said rf coil means to inductively
couple said rf electrical energy into the vacuum chamber; and
decoupling means for decoupling said sputter power source means
from said rf power source means.
12. The apparatus for depositing a material onto a substrate in a
vacuum chamber as defined in claim 1, wherein:
said magnet means comprises a plurality of ring shaped magnets;
and
said sputter means comprises a plurality of ring shaped targets
disposed between said ring shaped magnets and a sputter power
supply for providing power to said sputter targets to cause
sputtering thereof.
13. An apparatus for depositing a material onto a substrate in a
vacuum chamber comprising:
a first sputter target;
first sputter power source means for providing electrical energy to
said first sputter target for causing sputtering thereof;
first magnet means for providing a multidipole magnetic field for
magnetic confinement of plasma electrons in close proximity to the
sputtering surface of said first sputter target;
a hollow, cylindrical, second sputter target disposed between said
first sputter target and the substrate;
second sputter power source means for providing electrical energy
to said second sputter target for causing sputtering thereof;
second magnet means for providing a multidipole magnetic field for
magnetic confinement of plasma electrons in close proximity to the
sputtering surface of said second sputter target;
rf coil means disposed in the vacuum chamber for inductively
coupling rf energy into the vacuum chamber directly for producing a
plasma of sufficient density and volume to cause ionization of
sputtered atoms therein;
rf power source means for providing rf energy to said rf coil
means;
bias means for providing electrical bias to the substrate for
controlling the direction and energy of ions impinging thereon;
and
substrate placement means for placing the substrate in contact with
said plasma.
14. The apparatus for depositing a material onto a substrate in a
vacuum chamber as defined in claim 13, wherein said rf coil means
comprises:
a coiled hollow tube; and
a plurality of magnets disposed within said hollow tube for
confining plasma away from said rf coil means.
15. An apparatus for depositing a material onto a substrate in a
vacuum chamber comprising:
an rf coil disposed in the vacuum chamber and composed at least
partly of the material;
sputter power source means for providing electrical energy to said
rf coil to cause sputtering of the material therefrom;
magnet means for providing a multidipole magnetic field for
confinement of plasma electrons in close proximity to said rf
coil;
rf power source for providing rf power to said rf coil to cause
said rf coil to inductively couple rf energy into the vacuum
chamber for producing a plasma of sufficient density and volume to
cause ionization of sputtered atoms;
decoupling means to decouple said sputter power source means from
said rf power source means;
bias means for providing electrical bias to the substrate for
controlling the direction and energy of ions impinging thereon;
and
substrate placement means for placing the substrate in contact with
said plasma.
16. An apparatus for depositing a material onto a substrate in a
vacuum chamber comprising:
a first sputter target;
first sputter power source means for providing electrical energy to
said first sputter target for causing sputtering thereof;
first magnet means for providing a multidipole magnetic field for
confining plasma electrons in close proximity to the sputtering
surface of said first sputter target;
a plurality of ring sputter targets disposed between said first
sputter target and the substrate;
second sputter power source means for providing electrical energy
to said ring sputter targets for causing sputtering thereof;
a plurality of ring magnet means disposed adjacent to said ring
sputter targets for providing a multidipole magnetic field for
confining plasma electrons in close proximity to the sputtering
surface of said ring sputter targets;
rf coil means disposed in the vacuum chamber for inductively
coupling rf energy into the vacuum chamber directly for producing a
plasma of sufficient density and volume to cause ionization of
sputtered atoms;
rf power source means for providing rf energy to said rf coil
means;
bias means for providing electrical bias to the substrate for
controlling the direction and energy of ions impinging thereon;
and
substrate placement means for placing the substrate in contact with
said plasma.
17. An apparatus for producing a plasma in a vacuum chamber
comprising:
rf power source means for providing rf energy;
hollow rf coil means for inductively coupling said rf energy into
the vacuum chamber; and
a plurality of magnets disposed within said rf coil means for
confining plasma away from said rf coil means.
18. The apparatus for producing a plasma in a vacuum chamber as
defined in claim 17, wherein said magnets are positioned with their
magnetization directed radially outward from the center of said
tube.
19. The apparatus for a vacuum chamber as defined in claim 17,
wherein said magnets are positioned with their magnetization
directed axially along the length of said tube.
20. A method of depositing a material upon a substrate in a vacuum
chamber comprising the steps of:
sputtering the material off of at least one target with magnetron
discharge;
inductively coupling rf electrical energy directly into the vacuum
chamber using a rf coil disposed in the vacuum chamber in order to
cause ionization of said sputtered material;
confining the plasma whereby produced using a multidipole magnetic
field; and,
placing the substrate in contact with said plasma.
21. The method of depositing a material upon a substrate in a
vacuum chamber as defined in claim 20, further comprising the step
of:
biasing the substrate to control the energy and directionality of
ions impinging on the substrate.
22. A method of depositing a material upon a substrate in a vacuum
chamber comprising the steps of:
sputtering the material off of at least one target with magnetron
discharge;
inductively coupling rf power directly into the vacuum chamber
using a rf coil disposed in the vacuum chamber in order to cause
ionization of said sputtered material;
confining the plasma thereby produced using a multidipole magnetic
field;
placing the substrate in contact with said plasma; and,
biasing the substrate to control the energy and directionality of
ions impinging on the substrate.
23. The method of depositing a material upon a substrate in a
vacuum chamber as defined in claim 20 or 22 further comprising the
step of adding CVD gas into the vacuum chamber.
24. The method of depositing a material upon a substrate in a
vacuum chamber as defined in claim 20 or 22, further comprising the
step of placing magnets inside said rf coil to confine plasma away
from at least part of said rf coil.
Description
TECHNICAL FIELD
This invention relates to the deposition of materials onto a
semiconductor substrate and more particularly, a high plasma
density, low pressure, low temperature, sputtering tool for
depositing materials uniformly into high aspect ratio holes or
trenches.
BACKGROUND ART
The ability to deposit materials into high aspect ratio (AR) holes
(holes with a depth to width ratio greater than one) on a
semiconductor substrate is becoming increasingly more important in
the semiconductor industry for back-end-of-line applications such
as the filling of inter-level vias.
Prior techniques used to deposit materials into high AR holes
include: chemical vapor deposition (CVD); electron cyclotron
resonance chemical vapor deposition (ECR CVD); plasma enhanced
chemical vapor deposition (PECVD) and rf sputtering.
CVD is undesirable for two reasons: (a) it is a relatively slow
process; and (b) high temperature substrate curing is required
following the deposition. High temperature curing is unfavorable
for large scale integrated (LSI) components.
ECR CVD and PECVD have been introduced to lower the required curing
temperatures. These techniques, however, are also undesirable
because the films produced often contain hydrogen, thereby making
them dimensionally unstable at elevated temperatures. Also, these
techniques, like all CVD processes, are slow processes that
restrain throughput.
Traditional rf sputtering does not fill high AR holes uniformly
because there is no directionality to the deposition. The sputtered
atoms in the plasma generated are primarily neutral (plasma
referred to as having a low ionization ratio). The resultant random
neutral atom impingment on the substrate causes sputtered material
to build up along the walls of the holes faster than the bottom
thereby producing a void in the filled hole (a condition referred
to as angel wings) which makes contact to the filled hole
unreliable. Also, the background gas (e.g. Argon) necessary to
support the process: a) causes back scattering of the sputtered
material which consequently reduces the transmission of this
material to the substrate; and b) gets incorporated into the films.
A further disadvantage to traditional rf sputtering is that it is
difficult to obtain a plasma density high enough to sputter at
energy efficient voltages for single substrate deposition.
The following three articles disclose some recent improvements to
traditional rf sputtering: 1) Ono, Takahashi, Oda, and Matsuo,
"Reactive Ion Stream Etching and Metallic Compound Deposition Using
ECR Plasma Technology", Symposium on VLSI Technology. Digest of
Technical Papers 1985 pp 84-85, Bus. Center Acad. Soc Japan (ONO);
2) Yamashita, "Fundamental characteristics of built-in
high-frequency coil-type sputtering apparatus", J.Vac.Sci.Technol.
A7(2), Mar/Apr 1989 pp 151-158 (YAMASHITA); and 3) Matsuoka and
Ono, "Dense plasma production and film deposition by new high-rate
sputtering using an electric mirror", J.Vac.Sci.Technol. A7(4),
Jul/Aug 1989 pp 2652-2656 (MATSUOKA).
ONO discloses an ECR plasma generator adapted for depositing metals
on a substrate by placing a cylindrical sputtering target around
the plasma stream at the plasma extraction window. Sputtered
particles are activated for film formation reaction in the high
plasma density region of magnetron mode discharge and in the plasma
stream. Film formation reaction is also enhanced by the moderate
energy ion bombardment irradiated by the plasma stream. This system
provides higher deposition rates than prior sputtering techniques,
but it doesn't provide directionality to the deposition (due to a
low ionization ratio) and therefore fails to provide a solution to
the aforementioned angel wing problem.
YAMASHITA discloses a sputtering system with a high-frequency
discharge coil placed between the target and the substrate holder.
This configuration can produce a plasma with a variable ionization
ratio of the sputtered atoms. High ionization ratio deposition is
not practical with this apparatus, however, because secondary
electrons generated by the ions impinge on the substrate and
thereby cause excessive substrate heating. Furthermore, high
deposition rates can only be achieved with this device when the
deposition is dominated by neutral atoms. Depositions dominated by
neutral atoms have no directionality and therefore cause angel
winging in high AR holes.
MATSUOKO discloses a sputtering system using an electric mirror
consisting of a planar target, a cylindrical target, a magnetic
coil, and a substrate plate. High plasma densities (of primarily
neutral atoms) in close proximity to the cylindrical target are
obtained by this configuration, but like the ONO configuration,
there is no directionality to the deposition and angel winging
occurs.
An efficient, reliable system to deposit materials into high AR
holes on semiconductor substrates which avoids the problems of the
previously mentioned systems is highly desirable.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide an improved
sputtering system for high rate material deposition.
Another object is to provide for a deposition system which can
uniformly fill high aspect ratio holes and trenches of
semiconductor substrates.
Yet another object is to provide for a deposition system which
functions at low pressures, low temperature and energy efficient
voltages.
According to the present invention, a rf sputtering apparatus
includes a circular end sputter target and a biased substrate at
opposite ends of a vacuum chamber. A cylindrical sputter target is
positioned between the end target and substrate. Rf or DC bias is
applied to the targets in order to produce sputtering. Permanent
magnets are placed in close proximity to the sputter targets to
cause magnetron discharges. A rf coil is disposed inside the
chamber to inductively couple rf power into the chamber to maintain
a high density plasma in order to ionize sputter neutrals and cause
the plasma to be more evenly distributed throughout the chamber.
The rf coil may be magnetized to prevent recombination of the
plasma with the surface of the coil.
The present invention produces good quality films at fast rates,
low pressure and low temperature. It is compact and easily
manufacturable and can be used to produce sputter ion deposition.
Also, the uniformity of deposition can be adjusted for different
requirements, including filling high AR holes.
These and other objects, features, and advantages of the present
invention will become more apparent in the light of the detailed
description of exemplary embodiments thereof, as illustrated by the
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross sectional, schematic drawing of a first
embodiment of a sputter system according to the present
invention.
FIG. 2 is a perspective, cross sectional, schematic drawing of a
first embodiment of a sputter system according to the present
invention.
FIG. 3 is a cross sectional view taken along line 3--3 of FIG.
1.
FIG. 4 is a cross sectional, schematic drawing of second embodiment
of a sputter system according to the present invention.
FIG. 5 is a cross sectional, schematic drawing of a third
embodiment of a sputter system according to the present
invention.
FIG. 6 is a cross sectional, schematic drawing of a fourth
embodiment of a sputter system according to the present
invention.
FIG. 7 is a side view of rf coil according to the present
invention.
FIG. 8 is a cross sectional view, taken along line 8--8 of FIG. 7,
of a first embodiment of a rf coil according to the present
invention.
FIG. 9 is a cross sectional view, taken along line 9--9 of FIG. 7,
of a second embodiment of a rf coil according to the present
invention.
BEST MODE FOR CARRYING OUT THE INVENTION
Referring now to FIG. 1, a sputter system 10 includes a vacuum
chamber 20, which contains a circular end sputter target 12, a
hollow, cylindrical, thin, cathode magnetron target 14, a rf coil
16 and a chuck 18, which holds a semiconductor substrate 19. The
atmosphere inside the vacuum chamber 20 is controlled through
channel 22 by a pump (not shown). The vacuum chamber 20 is
cylindrical and has a series of permanent, magnets 24 positioned
around the chamber and in close proximity therewith to create a
multipole field configuration near the interior surface 15 of
target 12. Magnets 26, 28 are placed above end sputter target 12 to
also create a multipole field in proximity to target 12. A singular
magnet 26 is placed above the center of target 12 with a plurality
of other magnets 28 disposed in a circular formation around magnet
26. For convenience, only two magnets 24 and 28 are shown. The
configuration of target 12 with magnets 26, 28 comprises a
magnetron sputter source 29 known in the prior art, such as the
Torus-10E system manufactured by K. Lesker, Inc.. A sputter power
supply 30 (DC or rf) is connected by a line 32 to the sputter
target 12. A rf supply 34 provides power to rf coil 16 by a line 36
and through a matching network 37. Variable impedance 38 is
connected in series with the cold end 17 of coil 16. A second
sputter power supply 39 is connected by a line 40 to cylindrical
sputter target 14. A bias power supply 42 (DC or rf) is connected
by a line 44 to chuck 18 in order to provide electrical bias to
substrate 19 placed thereon, in a manner well known in the prior
art.
Power supplies 30, 39 cause atoms to be sputtered off of targets
12, 14, as is well known in the prior art. Sputter targets 12, 14
must therefore be made of the material to be deposited on the
substrate, such as copper. Rf coil 16 must also either be made of,
or coated with the deposition material in order to prevent
contamination of the deposited film.
The magnets 24 create static B fields which extend into the vacuum
chamber 20 and form "cusps" (46 in FIG. 3) near the interior
surface 15 of cylindrical target 14. The close proximity of
cylindrical sputter target 14 to the multipole magnets 24 leads to
regions of intense magnetron discharges between these cusps. An
illustration of the magnetic cusps and their effect upon the
cylindrical target sputtering is provided in more detail in FIG. 3.
Magnets 26, 28 placed above target 12 create magnetron discharges
at that target in a similar manner.
Material is sputtered off targets 12,14 when these targets are
provided either DC bias or rf power from respective power supplies
30, 39. The regions (48 in FIG. 3) near the interior surface of
cylindrical target 14 adjacent to the magnets will sputter quickly,
since plasma ions preferentially escape through the aforementioned
magnetic cusps, leading to high plasma density and high sputter
rates in the cusps. Cylindrical target 14 will also sputter quickly
in the regions between the magnets because the magnetic field
(which is parallel to the wall between the magnets) will give rise
to a magnetron discharge. The high plasma densities associated with
magnetron discharges will produce a high sputter rate from
cylindrical target 14 between the magnetic cusp regions (46 in FIG.
3) and a large fraction of neutral sputtered atoms will be ionized
in the high density rf plasma.
Power provided by rf power supply 34 is transmitted on line 36
through matching network 37 to rf coil 16, and thereby inductively
coupled into the aforementioned plasma in order to sustain the
plasma and cause a more even plasma distribution throughout the
vacuum chamber 20. A variable impedance 38 may be placed in series
with the rf coil 16 to control the rf voltage on the coil.
The plasma created by the present invention will have a high
ionization fraction of sputtered atoms due to: a) ionization by
primary electrons; b) ion charge exchange with the sputtering gas
ions (e.g. Argon ions); and c) Penning ionization of the sputtered
atoms by the sputtering gas. Penning ionization is particularly
sensitive to the chamber pressure (part of which is attributable to
sputter gas pressure), with optimum pressure ranging from 10 mTorr
to 50 mTorr. If the pressure is too high, the sputtered atoms
diffuse back into the target, thereby lowering the effective
deposition rate. Also, the plasma density will be lowered which
will reduce the amount of power coupled to the plasma. If the
pressure is too low, Penning ionization will stop altogether.
The DC or rf bias provided by voltage source 42 to the substrate 19
will determine the directionality of the deposition because the
bias affects a) the trajectories of the ionized sputtered atoms;
and b) the amount of resputtering. Consequently, the trajectories
of the ions can be adjusted such that high AR holes in the
substrate may be uniformly filled without angel winging effects. In
addition, heavier gases (gases with an atomic mass greater than the
atomic mass of the sputtered material), such as Xenon, may be added
to the vacuum chamber to further affect the deposition profile by
reducing angel winging effects. Also, the uniformity of deposition
can be adjusted by changing the voltage or power split between the
targets 12, 14 because cylindrical target 14 produces the highest
deposition rate on the outside part of substrate 19 and the target
12 produces the highest deposition rate on the inside part of
substrate 19.
Another advantage to the present invention is that the magnetic
fields created by magnets 26, 28 confine free electrons produced by
the end sputter target 12, thereby lowering secondary electron heat
loading of the substrate 19.
Referring now to FIG. 2, sputter targets 12,14 are provided power
by respective sources 30,38, (which may be DC or rf) to cause
material to be sputtered into vacuum chamber 20. Magnets 24 cause
regions 48 of intense plasma in close proximity to the interior
surface 15 of target 14. Rf power provided by source 34 is
inductively coupled into the plasma through coil 16. Bias applied
by voltage source 42 through line 44 to chuck 18 will attract
ionized atoms onto substrate 19 and facilitate directional
deposition.
Referring now to FIG. 3, magnets 24 create a static multipole B
field, represented by flux lines 46. This field acts in conjunction
with secondary electrons from targets 12,14 to create intense,
magnetron discharge, plasma regions as represented by the shaded
areas 48. Other names used for this type of field include
multipolar, multicusp or multidipole.
Referring now to FIG. 4, a second embodiment of the present
invention includes a rf coil 16 which is used as the sole sputter
source of a deposition apparatus by providing DC bias to the coil
using a DC source 50 coupled through a rf decoupling network 52,
comprising a capacitor 53 and inductors 54, 55. Rf coil 16, of
course, must either be manufactured from or coated with the desired
sputter material. Rf power is supplied to the coil through line 58
using rf power supply 60 and matching network 57. A variable shunt
impedance 56 may be used to control the rf voltage on coil 16. In
the absence of this shunt, the cold end 17 of coil 16 must be
capacitively connected to ground (i.e. by replacing shunt 56 with a
large capacitor). A plurality of magnets 62, (only two of which are
shown), are placed around the vacuum chamber 20. The resultant
magnetic fields 62 create surface magnetic confinement of plasma
electrons, thus producing an intense plasma and thereby causing a
high ionization ratio of the neutral sputtered atoms. These ions
are directionally accelerated toward the biased substrate 19, which
is controlled by DC or rf bias supply 42 through line 44.
Referring now to FIG. 5, a third embodiment of the present
invention includes a circular end sputter target 66 and a
cylindrical, hollow, cathode magnetron sputter target 68 contained
within vacuum chamber 70. Power sources 30,38 provide electrical
energy necessary to cause sputtering of respective targets 66,68 as
previously described. Electromagnets 74 create magnetron discharges
adjacent to target 68 and thereby produce a high fraction of
sputter material ions which are accelerated towards the biased
substrate 19. Voltage source 42 biases substrate 19 through line
44. A microwave power source (not shown) provides microwave energy
through wave guide 72 and is a substitute power source for the rf
coil 16 used in previously described embodiments. The resultant
plasma can be maintained by: a) microwave power (as in an "ECR"
type plasma); b) ri or DC voltage applied to the targets; c) rf
induction; and d) Whistler waves, all of which may be used
singularly or in combinations thereof. The uniformity of deposition
can be adjusted by changing the voltage or power between the end
target 66 and cylindrical magnetron target 68 because the
cylindrical target 68 produces the highest deposition rate on the
outside part of substrate 19 and the end target 66 produces the
highest deposition rate on the inside part of substrate 19.
Electromagnets 74 are used in the third embodiment because it is
necessary to have a strong B field (about 0.1 Tesla) over the
majority of the chamber volume. The other embodiments of the
present invention described herein require only strong localized B
fields in close proximity to the sputter targets. Permanent magnets
are therefore acceptable as the B field source although
electromagnets could very well be used in there place.
Referring now to FIG. 6, a fourth embodiment of the present
invention includes a rf coil 16, rf supply 34, matching network 37,
variable series impedance 38, chuck 18, substrate 19, and bias
supply 42 used in conjunction with a series of ring-type sputter
targets 76 and magnets 78. The sputter targets 76, 77 are biased by
signal sources 80, 30 through lines 82,32 respectively. Ring
magnets 78 are radially magnetized. The combination of ring targets
76 and ring magnets 78 produce a multipole, magnetron discharge
effect. Intense magnetron discharges (represented by shaded
patterns 86) will occur in the spaces between the multipole
magnetic cusps (represented by flux lines 88). Since the rf coil 16
is actually located in the vacuum vessel, auxiliary magnets 26, 28
may be placed on the top and bottom of the chamber 20 to increase
the plasma confinement and to create additional regions of
magnetron discharge. The sputtered material will be deposited on
substrate 19, which is biased by supply 42. The bias on the
substrate will determine the directionality of the deposition
because it affects the trajectories of the ionized sputtered
atoms.
The ions produced in vacuum chamber 20 of all of the aforementioned
embodiments of the present invention, as illustrated in FIGS. 1-6,
which strike the substrate 19 will have low angular divergence
after crossing the plasma sheath and therefore will fill high AR
holes uniformly.
Furthermore, the temperature of the chuck 18 and substrate 19 can
be controlled by any of the standard methods well known in the
prior art, including electrostatic clamping with backside helium
gas conduction.
Also, it is to be noted that the aforementioned embodiments of the
present invention provide for high plasma densities (greater than
10.sup.11 cm.sup.-3) to be distributed throughout a major portion
of the vacuum chamber.
Furthermore, low pressures (e.g. 0.02 to 10 mTorr) of CVD gas may
also be used to increase system pressure and deposition rates. In
this "CVD/sputter" mode, the volatiles (e.g. hydrogen) may be
pumped away while the desired components are maintained in the
plasma (by sputtering from the targets 66,68) until they are
deposited on the substrate 19. The particular amount of
resputtering and the energy per ion necessary to obtain desired
film properties may be changed by varying the rf bias to the
substrate 19. Also, the high plasma density generated makes it
possible to turn off the flow of sputtering gas (e.g. Argon) and
sustain the plasma by impact of ionized sputtered atoms onto the
sputter target self-sputtering). In the case of metal sputter
targets, this facilitates the generation of pure metal plasmas,
which enables high deposition rates and allows the present
invention to be used as a single substrate tool. The use of pure
metal plasma also favorably affects the physical properties (i.e.
absence of impurities) of the sputter grown films.
Referring now to FIG. 7, rf coil 16 includes a hollow tube 90
having permanent magnets (92 or 94) disposed inside. Placing
magnets (92 or 94) inside the tube accomplishes three things: 1) it
reduces the plasma loss area (due to recombination of the sputtered
atoms with the coil) to the magnetic pole area; 2) it produces
crossed dc and rf magnetic fields which can drive the plasma
through Whistler mode plasma waves; and 3) it reduces the
capacitive coupling losses of the coil.
Referring now to FIG. 8, permanent magnets 92 may be disposed
inside tube 90 with their magnetization directed radially outward
from the center of the tube to thereby produce line cusps (not
shown) along the length of the tube.
Referring now to FIG. 9, permanent magnets 94 may also be disposed
inside tube 90 with their magnetization directed axially along the
tube to thereby produce ring cusps (not shown) at each pole
face.
Use of magnets inside rf coil 16 allows the plasma to run at lower
pressure, higher efficiency, and higher plasma density. This coil
design may also be applied to other inductive coil sputter systems
not described herein, including internal or external coil
systems.
Although the invention has been shown and described with exemplary
embodiments thereof, it should be understood by those skilled in
the art that the foregoing and various other changes, omissions and
additions may be made therein and thereto without departing from
the spirit and scope of the invention.
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